Prediction of the morphology of the as-implanted damage in silicon using a novel combination of BCA and MD simulations

Abstract

In order to predict type and amount of defects created by keV ions under realistic implantation conditions, a combination of computer simulations based on the binary collision approximation (BCA) with classical molecular dynamics (MD) calculations is proposed. Time-ordered BCA simulations are applied to ballistic processes with characteristic energies above several 10 eV. Athermal, rapid thermal, and thermally activated processes with lower characteristic energies are treated by MD simulations. They yield the as-implanted defect state formed several 10 ps after ion impact. The MD calculations are performed in cells which are much smaller than the entire volume of the collision cascade of an incident ion but much larger than the distance between nearest-neighbor atoms in the lattice. The as-implanted damage produced by a single ion in a certain cell is found to be completely determined by the nuclear energy deposition of the ion into the cell. Therefore, the MD calculations need to be performed only in one cell for different values of nuclear energy deposition, and statistical considerations based on BCA simulations can be employed to obtain the depth profile and the total number of different defect species (vacancies, interstitials, disordered atoms, etc.) created on average per incident ion. The novel simulation method is applied to investigate the damage morphology produced by 15 keV B +, 30 keV P +, and 15 keV As + implants.